내부 냉각유로에서 열전달 강화와 압력손실 감소를 위한 표면 형상체의 개발

두정훈(Jeong Hoon Doo),윤현식(Hyun Sik Yoon),하만영(Man Yeong Ha) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

A new surface shape of an internal cooling passage which largely reduces the pressure drop and enhances the surface heat transfer is proposed in the present study. The surface shape of the cooling passage is consisted of the concave dimple and the riblet inside the dimple which is protruded along the stream-wise direction. Direct Numerical Simulation (DNS) for the fully developed turbulent flow and thermal fields in the cooling passage is conducted. The Numerical simulations for the 5 different surface shapes are conducted at the Reynolds number of 2800 based on the mean bulk velocity and channel height and Prandtl number of 0.71. The driving pressure gradient is adjusted to keep a constant mass flow rate in the x direction. The thermoaerodynamic performance for the 5 different cases used in the present study was assessed in terms of the drag, Nusselt number, Fanning friction factor, Volume and Area goodness factor in the cooling passage. The value of maximum ratio of drag reduction is -22.86 [%], and the value of maximum ratio of Nusselt number augmentation is 7.05 [%] when the riblet angle is 60˚ (Case 5). The remarkable point is that the ratio of Nusselt number augmentation has the positive value for the surface shapes which have over 45˚ of the riblet angle. The maximum Volume and Area goodness factor are obtained when the riblet angle is 60˚ (Case 5).

내부 냉각유로에서 열전달 강화와 압력손실 감소를 위한 표면 형상체의 개발

두정훈(Jeong Hoon Doo),윤현식(Hyun Sik Yoon),하만영(Man Yeong Ha) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.6

A new surface shape of an internal cooling passage which largely reduces the pressure drop and enhances the surface heat transfer is proposed in the present study. The surface shape of the cooling passage is consisted of the concave dimple and the riblet inside the dimple which is protruded along the stream-wise direction. Direct Numerical Simulation (DNS) for the fully developed turbulent flow and thermal fields in the cooling passage is conducted. The numerical simulations for five different surface shapes are conducted at the Reynolds number of 2800 based on the mean bulk velocity and channel height and Prandtl number of 0.71 . The driving pressure gradient is adjusted to keep a constant mass flow rate in the x direction. The thermoaerodynamic performance for five different cases used in the present study was assessed in terms of the drag, Nusselt number, Fanning friction factor, volume and area goodness factor in the cooling passage. The value of maximum ratio of drag reduction is -22.86 % , and the value of maximum ratio of Nusselt number augmentation is 7.05% when the riblet angle is 60°. The remarkable point is that the ratio of Nusselt number augmentation has the positive value for the surface shapes which have over 45° of the riblet angle. The maximum volume and area goodness factors are obtained when the riblet angle is 60°.

돌출부를 포함한 딤플 표면을 가진 냉각 유로에서의 유동과 열전달 성능 향상에 관한 수치적 연구

김정은(Jeong Eun Kim),하만영(Man Yeong Ha),윤현식(Hyun Sik Yoon),두정훈(Jeong Hoon Doo) 대한설비공학회 2011 설비공학 논문집 Vol.23 No.12

In the present study, the detailed flow structure and heat transfer characteristics in the newly-designed heat transfer surface geometry were investigated. The surface geometry proposed in the present study is a traditional dimple structure combining with a protrusion inside the dimple, which is named a protrusion-in-dimple in this study. The basic idea underlying the present surface geometry is to enhance the flow mixing and the corresponding heat transfer in the flow re-circulating region generated by a conventional dimple cavity. The present study was performed by the direct numerical simulation at a Reynolds number of 2800 based on mean velocity and channel height and Prandtl number of 0.71. Three different protrusion heights for protrusion-in-dimples were considered as the main design parameter of the present study. The calculated pressure drop and heat transfer capacity were assessed in terms of the Fanning friction factor and Colburn j factor. The overall performances estimated in terms of the volume and area goodness factor for protrusion-in-dimple cases were higher than the conventional dimple case.

압력손실 및 열전달 성능 향상을 위한 열전달 표면의 설계에 대한 수치적 연구

김정은(Jeong Eun Kim),하만영(Man Yeong Ha),윤현식(Hyun Sik Yoon),두정훈(Jeong Hoon Doo) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

In the present study, the detailed flow structure and heat transfer characteristics in the newly-designed heat transfer surface geometry were investigated using three dimensional direct numerical simulations. The surface geometry proposed in the present study was modified on the basis of a conventional dimpled surface shape, which is named a protrusion-in-dimple. The configuration of protrusion-in-dimple is made up of a dimple cavity and a single center-aligned protrusion structure inside the dimple cavity. The basic idea underlying the present surface geometry is to enhance the flow mixing and the corresponding heat transfer in the flow recirculating region generated by a conventional dimple cavity. The parametric study was performed for the present surface geometries having three different protrusion heights which is compared with a general dimple at the Reynolds number of 2800 based on the mean fluid velocity and channel height and Prandtl number of 0.71 (air)

회전하는 원형 실린더 주위의 층류 유동장에 관한 수치적 연구

이용석(Yong Suk Lee),두정훈(Jeong Hoon Doo),하만영(Man Yeong Ha),윤현식(Hyun Sik Yoon) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

The present study numerically investigates three-dimensional laminar flow past a rotating circular cylinder placed in a uniform stream. For the purpose of a careful analysis of the modification of flow by the effect of the rotation on the flow, numerical simulations are performed at a various range of rotational speeds (0≤α≤2.5) at one Reynolds number of 300. As α increases, flow becomes stabilized and finally a steady state beyond the critical rotational speed. The 3D (three dimensional) wake mode of the stationary cylinder defined at this Reynolds number has been disorganized according to α, which were observed by the visualization of 3D vortical structures. The variation of the Strouhal number is significant when the wake pattern is changed according to the rotational speed. As α increases, the lift increases, whereas the drag decreases.

원형실린더 주위의 강제대류에 미치는 실린더 형상변화의 수치적 연구

김민호(Min Ho Kim),윤현식(Hyun Sik Yoon),하만영(Man Yeong Ha),두정훈(Jeong Hoon Doo) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.5

Numerical simulations are performed in order to investigate the effect of the shape modification on the forced convection around a circular cylinder at the Reynolds number of 300 and Prandtl number of 0.71 (air). The fractional step method based on the finite volume method was employed to solve the incompressible Navier-Stokes equations in the generalized coordinate system. Three-dimensional characteristics of fluid flow and heat transfer around circular, elliptic and wavy cylinders are investigated. An elliptic cylinder has elliptic cross section and a wavy cylinder has the sinusoidal variation in the cross sectional area along the spanwise direction. An elliptic cylinder has an axis ratio of 1.35 (major axis is 1.15 and minor axis is 0.85) and a wavy cylinder has the wave length of π/3 and wavy amplitude of 0.1. The present computational res비 ts for a ellipse cylinder and a wavy cylinder are compared with those for a circular cylinder. The drag and lift coefficient of the circular cylinder is larger than that of the elliptic cylinder and is similar to that of wavy cylinder. The time-and surface-averaged Nusselt number of the circular cylinder is larger than that of the elliptic cylinder and is similar to that of wavy cylinder. However, the total heat transfer rate for a wavy cylinder becomes larger than that for the circular cylinder because the wavy cylinder has larger wetted surface area than the circular cylinder.

회전하는 원형 실린더 주위의 층류 유동장에 관한 수치적 연구

이용석(Yong-Suk Lee),윤현식(Hyun-Sik Yoon),두정훈(Jeong-Hoon Doo),하만영(Man-Yeong Ha) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.11

The present study numerically investigates three-dimensional laminar flow past a rotating circular cylinder placed in a uniform stream. For the purpose of a careful analysis of the modification of flow by the effect of the rotation on the flow, numerical simulations are performed at a various range of rotational coefficients (0≤α≤2.5) at one Reynolds number of 300. As α increases, flow becomes stabilized and finally a steady state beyond the critical rotational coefficient. The 3D (three dimensional) wake mode of the stationary cylinder defined at this Reynolds number has been disorganized according to α, which were observed by the visualization of 3D vortical structures. The variation of the Strouhal number is very weak when the wake pattern is changed according to the rotational coefficient. As α increases, the lift increases, whereas the drag decreases.